Re: [PATCH v1 00/15] Add support for Nitro Enclaves

[Paraschiv, Andra-Irina]

On 22/04/2020 00:46, Paolo Bonzini wrote:
> On 21/04/20 20:41, Andra Paraschiv wrote:
> > An enclave communicates with the primary VM via a local communication channel,
> > using virtio-vsock [2]. An enclave does not have a disk or a network device
> > attached.
> Is it possible to have a sample of this in the samples/ directory?

I can add in v2 a sample file including the basic flow of how to use the 
ioctl interface to create / terminate an enclave.

Then we can update / build on top it based on the ongoing discussions on 
the patch series and the received feedback.

> I am interested especially in:
>
> - the initial CPU state: CPL0 vs. CPL3, initial program counter, etc.
>
> - the communication channel; does the enclave see the usual local APIC
> and IOAPIC interfaces in order to get interrupts from virtio-vsock, and
> where is the virtio-vsock device (virtio-mmio I suppose) placed in memory?
>
> - what the enclave is allowed to do: can it change privilege levels,
> what happens if the enclave performs an access to nonexistent memory, etc.
>
> - whether there are special hypercall interfaces for the enclave

An enclave is a VM, running on the same host as the primary VM, that 
launched the enclave. They are siblings.

Here we need to think of two components:

1. An enclave abstraction process - a process running in the primary VM 
guest, that uses the provided ioctl interface of the Nitro Enclaves 
kernel driver to spawn an enclave VM (that's 2 below).

How does all gets to an enclave VM running on the host?

There is a Nitro Enclaves emulated PCI device exposed to the primary VM. 
The driver for this new PCI device is included in the current patch series.

The ioctl logic is mapped to PCI device commands e.g. the 
NE_ENCLAVE_START ioctl maps to an enclave start PCI command or the 
KVM_SET_USER_MEMORY_REGION maps to an add memory PCI command. The PCI 
device commands are then translated into actions taken on the hypervisor 
side; that's the Nitro hypervisor running on the host where the primary 
VM is running.

2. The enclave itself - a VM running on the same host as the primary VM 
that spawned it.

The enclave VM has no persistent storage or network interface attached, 
it uses its own memory and CPUs + its virtio-vsock emulated device for 
communication with the primary VM.

The memory and CPUs are carved out of the primary VM, they are dedicated 
for the enclave. The Nitro hypervisor running on the host ensures memory 
and CPU isolation between the primary VM and the enclave VM.


These two components need to reflect the same state e.g. when the 
enclave abstraction process (1) is terminated, the enclave VM (2) is 
terminated as well.

With regard to the communication channel, the primary VM has its own 
emulated virtio-vsock PCI device. The enclave VM has its own emulated 
virtio-vsock device as well. This channel is used, for example, to fetch 
data in the enclave and then process it. An application that sets up the 
vsock socket and connects or listens, depending on the use case, is then 
developed to use this channel; this happens on both ends - primary VM 
and enclave VM.

Let me know if further clarifications are needed.

> > The proposed solution is following the KVM model and uses the KVM API to be able
> > to create and set resources for enclaves. An additional ioctl command, besides
> > the ones provided by KVM, is used to start an enclave and setup the addressing
> > for the communication channel and an enclave unique id.
> Reusing some KVM ioctls is definitely a good idea, but I wouldn't really
> say it's the KVM API since the VCPU file descriptor is basically non
> functional (without KVM_RUN and mmap it's not really the KVM API).

It uses part of the KVM API or a set of KVM ioctls to model the way a VM 
is created / terminated. That's true, KVM_RUN and mmap-ing the vcpu fd 
are not included.

Thanks for the feedback regarding the reuse of KVM ioctls.

Andra




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